1. Field of the Invention
The present invention relates to a cryopump and an evacuation method.
2. Description of the Related Art
A cryopump is a vacuum pump that captures and pumps gas molecules by condensing or adsorbing molecules on a cryopanel cooled to an extremely low temperature. A cryopanel is generally used to achieve a clean vacuum environment required in a semiconductor circuit manufacturing process.
For example, cited document 1 describes a cryopump provided with a plurality of elongated panels mounted in a radial pattern on the back of a heat shield panel with respect to the direction in which the gas is introduced and extending backward from the heat shield panel. [patent document No, 1] JP 2-308985
In the aforementioned cryopump, a heat shield panel is provided close to and opposite to the opening through which the gas to be pumped is introduced. The heat shield panel restricts the flow of gas to the cryopanels below so that the pumping speed of the cryopump is lowered accordingly. Since the heat shield panel with a relatively large area that occupies the major part of the cross section of the cryopump is provided close to the opening of the cryopump, a large amount of radiant heat is input from outside. For this reason, energy consumption required to cool the cryopanels sufficiently will be increased. Further, the temperature of the cryopanels may be increased and the pumping performance may be adversely affected.